1. Field of the Invention
The present invention relates to a method for image alignment of breast images.
2. Description of the Related Art
Radiologists examine mammographic images to diagnose various abnormalities in a breast. The images are nowadays examined on a display device such as the display screen of a computer workstation.
Essential for a mammographic display system is the ability of the radiologist to quickly analyze the mammographic images of the breast and create a report of his diagnosis.
Analyzing breast images often comprises comparing breast images by aligning two or more breast images. These images may be images of the same object acquired at different times and/or with different display settings or images of right and left breast etc.
The conventional procedure to achieve such an alignment is based on nipple alignment or pectoralis alignment. Mostly, for craniocaudal (CC) images, the nipple is located in each pair of images and the images are positioned such that the nipple is located at the same height (see FIG. 2). For mediolateral-oblique (MLO) images, either nipple or pectoralis alignment is used (see FIG. 3). While both methods generate similar results, it is possible that the alignment is different when the position of the breasts during the acquisition differs (see FIG. 4).
The observation that pectoralis alignment can be suboptimal in combination with the fact that accurate nipple detection is not always possible, is an indication that more robust alignment methods are desirable. Radiologists prefer aligned images because it facilitates comparison of the images. Aligned images are most similar to mirrored images for which our eyes and brains are trained to find differences. Alignment based on a few key features, being the nipple or the pectoralis muscle, is not optimal.
U.S. Pat. No. 7,885,443 as well as US 2011/0128289 disclose a method for facilitating temporal comparison of breast mammograms by a viewer. A first and a second mammogram are displayed at identical tissue distance per unit display distance in a number of display windows sized and paired according to a hanging protocol. A fiducial alignment marker location is identified in the breast tissue area of each of the mammograms. Paired ones of the displayed mammogram views are displayed horizontally adjacent to each other and are vertically aligned on said mammogram display according to said identified fiducial marker locations.
It is an aspect of the present invention to provide a method for optimal alignment of breast images so as to facilitate optimal analysis of breast images.